Communication of information is an endemic need of modern society. A communication system is used through which to communicate the information. A communication system includes, at a minimum, a set of communication stations including a sending station and a receiving station. The communication stations are interconnected by way of a communication channel. If necessary, the sending station first converts the information into a form to permit its communication upon the communication channel. And, correspondingly, at the receiving station, the receiving station converts the received information into a form to facilitate the recovery of its informational content.
Many different types of communication systems have been developed and implemented to communicate data pursuant to many different types of communication services. As technological advancements permit, improvements to existing communication systems, and implementation of new types of communication systems, shall likely be possible.
A radio communication system is an exemplary type of communication system. A radio communication system is a type of communication system in which communication channels are defined upon radio links extending between the communication stations thereof. Radio communication systems provide several advantages over their wireline counterparts. The infrastructure costs associated with initial implementation and deployment of a radio communication system are generally lower than the corresponding costs associated with implementation and deployment of a wireline counterpart. And, a radio communication system is amenable for implementation as a mobile communication system. Because radio links, rather than wireline connections, are used to interconnect the communication stations, the communication stations need not be positioned at a fixed location.
A cellular communication system is a type of radio communication system that has achieved significant levels of popular usage. The network infrastructures of cellular communication systems have been installed throughout significant portions of populated areas of the world. The cellular communication systems are constructed, generally, pursuant to selected operating standards promulgated by standard-setting bodies. Such operating standards set forth, amongst other things, the operational parameters of the elements of the communication systems and the signaling generated during their operation.
The network infrastructure of a cellular communication system includes base transceiver stations that are positioned at selected locations throughout a geographical area to be encompassed by the communication system. Each base transceiver station defines an area, referred to as a cell, and a cellular communication system derives its name from such a designation.
Telephonic communications are effectuated between the base transceiver stations and mobile stations. Mobile stations are portable transceivers capable of detecting and transmitting signals upon the radio channels defined in the cellular communication systems. Access by a mobile station to communicate with the network infrastructure is generally granted pursuant to a service subscription. Users of mobile stations are, accordingly, sometimes referred to as subscribers, and the mobile stations are sometimes referred to as subscriber stations.
In an ideal communication system, the values of information, i.e., data, received at a receiving station are identical to corresponding values transmitted by a sending station. That is to say, the communication channel is distortion-free and does not distort the values of the data when communicated thereon. But, in an actual communication system, the data, operated upon at a receiving station, might well differ in value with the corresponding values when sent by a sending station. If the distortion is significant, the informational content of the data cannot be recovered at the receiving station.
Fading conditions upon the communication channel is a source of distortion of the data communicated upon the communication channel. If the level of fading is significant, the informational content of the data might not be able to be recovered.
The distortion caused by fading is compensated for by various techniques. Space diversity, for instance, is sometimes utilized. Space diversity is created at a sending station through the use of more than one transmit antenna from which data is converted into electromagnetic form and sent upon separate communication paths to a receiving station. Spatial redundancy is provided through the use of multiple transmit antennas. The separation distances separating the transmit antennas are selected in manners better to ensure that the signals transmitted from the respective transmit antennas fade in uncorrelated manners. Receiving stations also sometimes are formed to include multiple receive antennas, also typically separated by selected separation distances.
Radio communication systems that utilize multiple antenna configurations at the sending and receiving stations are sometimes referred to as MIMO (Multiple Input, Multiple Output) systems. Communications in an MIMO system permit higher overall communication capacities relative to conventional systems that utilize only single-antenna configurations.
OFDM (Orthogonal Frequency Division Multiplexing) communication techniques are amenable for use in an MIMO communication system. OFDM communication techniques facilitate mitigation of the effects of frequency selective fading. In such a technique, a set of frequency subcarriers are formed in which each of the subcarriers exhibits flat fading conditions. An MIMO-OFDM system, i.e., an MIMO communication system that utilizes OFDM communication techniques, is able to achieve high data rates as separate data, communicated upon separate subcarriers, is communicated concurrently by a sending station to a receiving station.
Channel conditions upon the separate subcarriers are uncorrelated, and different ones of the subcarriers exhibit different fading conditions. And, the recovery of the informational content of the data sent upon different ones of the subcarriers is achieved with different levels of effort. The overall performance of an MIMO-OFDM system, however, is dominated by the communication performance data communicated upon the weaker subcarriers. Operations at the receiving station to recover the informational content of the data, in a common manner, oftentimes is an inefficient manner by which to recover the informational content of the data.
If a manner could be provided by which to take into account the communication conditions upon the individual subcarriers, or channels otherwise defined, improved efficiency of receiving station operation would be provided.
It is in light of this background information related to communications in an MIMO communication system that the significant improvements of the present invention have evolved.